Heat oil in a 6-quart pressure cooker over medium heat until hot, Add rice and onion, and saute 1 minute, Stir in wine and broth, Close lid securely, and bring to high pressure over high heat (about 4 minutes), Adjust heat to medium or level needed to maintain high pressure, and cook 3 minutes,______, Place pressure cooker under cold running water, Remove lid, and stir in the tomatoes, parsley, pepper, and prosciutto, Cook, uncovered, over medium-high heat 3 minutes, stirring constantly, Stir in cheese, Garnish with parsley sprigs, if desired,